Recent development of some OTP products, such as flash drives, LCD-drivers and the like, has incurred an increase in programming voltage from the 3.3 volt level to 8.5 volts. The purpose of the ESD protection device is to protect victims and bypass ESD current during an electrostatic discharge event. The typical ESD protection device, such as an NMOSFET circuit provided for 3.3 volt applications, presents reliability issues if applied to the higher voltage devices. Gate-drain oxide breakdown in FET circuitry is a likely possibility.
Moreover, the protection circuit should not turn on under normal and programming operation modes. Normally, the junction breakdown of 3.3V devices is around 9.7V. For an 8.5V programming voltage OTP application, the Vt1 “trigger voltage” of an ESD device can't be lower than the programming voltage; otherwise the ESD device will cause a false trigger, thus interfering with normal and programming operation modes.
A critical need thus exists for an ESD protection device for one-time programmable products that is highly reliable and immune to false-triggering under a high damping noise environment or under a latch-up testing environment. Such a protection device should operate at a voltage margin that can accommodate, for example, programming timing of about 50 μs pulse width with 10 μs rise time. The trigger voltage should be set at a level that adequately protects the circuit during electrostatic discharge to divert discharge current between supply terminals, but at a level that prevents diversion of current during the relatively high voltage programming operation for one-time programmable (OTP) devices.